Parenteral liquids such as normal saline, 5% dextrose, etc. are frequently administered to a patient from a bottle hanging above the patient which is connected to a flexible tube having at its lower end a needle penetrating the patient's vein. This is frequently referred to as intravenous (I.V.) administration or feeding.
During this administration it is important not to inject any air into the patient's vein as this could cause a serious embolism. One proposal for eliminating any air bubbles or other entrapped air from the administered liquid is described in the Riely U.S. Pat. No. 3,631,654 in which a Y type connector has two dissimilar filters, one passing air, but not liquid, to the atmosphere through one branch; and the other filter passing liquid, but not air, to the patient delivery line. Such type filters sometimes encounter problems with large head pressures created by the hanging bottle causing the air venting filter to seep liquid to the atmosphere.
To provide a more positive control over extraction of the gas, it has been proposed by others, O'Leary et al U.S. Pat. No. 3,905,905 to use a single filter which passes liquid, but not gas, to separate out the gas into a gas collection chamber. Such filter would also filter out any particulate matter that may be in the administration liquid. Rather than automatically venting the collected air or gas to the atmosphere, O'Leary et al periodically extracts it with a hypodermic syringe that pierces a puncturable diaphragm into the gas collecting chamber. In the O'Leary et al device the extraction needle is inserted in very close relationship to the filter membrane so substantially all of the air or gas collected directly above the membrane can be extracted through the syringe needle. Great care must be taken to prevent cocking of the extraction needle and thereby gouging and damaging the filter membrane which could allow both gas and particulate matter to flow through the filter membrane.